Question: $(1 - \cos^2\theta)(\cos^2\theta) = \; ?$
Explanation: We can use the identity ${\sin^2 \theta} + {\cos^2 \theta} = 1$ to simplify this expression. $1$ ${\sin\theta}$ ${\cos\theta}$ $\theta$ We can see why this is true by using the Pythagorean Theorem. So, $1 - \cos^2\theta = \sin^2\theta$ Plugging into our expression, we get $ (1 - \cos^2\theta)(\cos^2\theta) = (\sin^2\theta)(\cos^2\theta) $ This is $\cos^2\theta \cdot \sin^2\theta$.